Some magnetic resonance imaging (MRI) techniques are pushing MRI apparatus towards their performance limits. Acquisition techniques that operate near the limits may be sensitive to small gradient field perturbations that may create image artifacts. Some conventional MRI acquisitions can successfully rely on a long-standing assumption that the gradient field produced by an MRI apparatus accurately matches the gradient field that was intended to be produced by the MRI apparatus. These conventional MRI acquisitions can rely on the assumption because small field perturbations may be tolerated in image reconstruction. However, some MRI acquisitions that push the MRI apparatus towards their performance limits may not rely on the assumption because even small field perturbations may produce unacceptable artifacts that cannot be tolerated in image reconstruction.
Magnetic field monitoring (MFM) is known to MRI. In theory, MFM can be employed to measure magnetic field perturbations directly and thus can be employed to account for (e.g., correct) artifacts produced by the magnetic field perturbations. While MFM is theoretically able to produce these results, practical implementations of MFM have faced several challenges. For example, conventional MFM has employed a network of miniature MRI coils with highly localized sensitivities to measure the magnetic field evolutions at different spatial locations. If the spatial locations have an appropriate spatial distribution, then the field dynamics can be calculated accurately in an imaging volume. But the network of small coils requires extra cabling, circuitry, and other equipment that may be difficult to accommodate.
Some conventional MFM systems may have relied on an NMR signal from hydrogen to monitor magnetic field dynamics. But for MFM to work, the MFM signal can only come from the local signal source (e.g., MFM probe). If there is any coupling between the MFM signal from different probes in different spatial locations, or if there is any coupling between MFM signal and an NMR signal from an imaging subject, then the MFM system will produce incorrect measurements. Conventional MFM systems may, therefore, have tried to reduce the likelihood of coupling between signals for different probes by spacing probes far apart.
Receive only arrays for MFM have limitations. Therefore, some conventional MFM systems have employed an array of hetero-nuclear transceiver probes to address these limitations. Unfortunately, using an array of hetero-nuclear transceiver probes introduces a requirement for a separate, specialized, multi-frequency transceiver system that is able to acquire, process, and provide the MFM signals from the array of hetero-nuclear transceiver probes.